The long term objective of this research is to study how information about head tilt and head rotation is processed by the vestibular peripheral end organs. It has become clear that the biomechanics of the cupula--endolymph and otoconial systems as well as the physiology of hair cells, synaptic processes and primary afferent terminals contribute to the signal processing that occurs in the end organs. In the past, investigators have monitored these contributions by studying responses of vestibular primary afferents during physiological and non- physiological stimulation. In this proposed research, we wish to focus our efforts on the hair cells of the semicircular canals and the utricle. In particular, we wish to study isolated solitary type I and type II hair cells from the adult pigeon's vestibular neuroepithelium and try to understand the role played by hair cells in the transduction process and in the transfer of information through the different neural elements of the vestibular neuroepithelium. We have develop procedures for identifying type I and type II hair cells that have been dissociated from the neuroepithelium. We have begun to study the currents and potentials in type I and type II hair cells form the cristae of the semicircular canals using whole cell patch clamp techniques. We wish to extend these studies and 1) characterize more fully the active and passive membrane properties of semicircular canal type I hair cells, 2) compare and contrast, in semicircular canal type I and type II hair cells, the mechanoelectric transduction (met) curents and the transfer function that relates stereociliary deflection and membrane potential, 3) compare and conrast the filtering properties of the basolateral membrane and semicircular canal type I and type II hair cells, and 4) study type I and type II hair cells from the utricle and compare their responses with those of hair cells from the semicircular canals. Finally, we wish to know if met currents, basolateral membrane currents and membrane filtering properties are different in different regions of the utricular maculae and semicircular canal cristae. The information obtained from studies meet the specific aims of this proposal may help us better understand certain phenomena related to inner ear pathology that involvew the hair cells such as ototoxicity, hydrops etc.